Plastic injection molding system with multiple tip torpedo heater

ABSTRACT

A plastic injection molding system having a plurality of multiple tip torpedo heaters which each have a casing with a pair of opposed tips disposed in respective sprue passageways in a mold. An unsheathed electrical heating element is disposed in an internal bore of the casing at each tip and heat transmitting material is compacted in the bore in surrounding relation to the heating element for electrically insulating each heating element from the casing and filling all air voids between the casing and heating element to effect direct heat transfer to the casing. Electrical leads couple the plurality of heating elements to a power source to permit independent temperature control of the individual heating elements and the exposed surfaces of the respective casing tips over which fluid plastic material is directed.

This is a division of application Ser. No. 913,020, filed Sept. 29,1986, now U.S. Pat. No. 4,755,126, which is a continuation in part ofapplication Ser. No. 817,008 filed Jan. 8, 1986 now abandoned.

DESCRIPTION OF THE INVENTION

The present invention relates generally to plastic injection moldingequipment, and more particularly, to an improved electrically heatedtorpedo for use in such equipment.

In plastic injection molding equipment it generally is necessary thateach passageway in the mold through which fluid plastic passes duringits travel to a mold cavity be heated to a predetermined substantiallyuniform temperature in order to enable the proper material flow. Forthis purpose, it is common to utilize sprue torpedo heaters, runnertorpedo heaters and the like in each passageway. In injection moldingequipment in which there is provided a plurality of mold cavities forsimultaneous molding of a plurality of parts, it usually is necessarythat the sprue passageways to each cavity be heated in such manner. As aresult, the number of mold cavities that can be included in theequipment can be limited by space considerations.

It is an object of the present invention to provide a relatively compactand more efficiently operable plastic injection molding system.

Another object is to provide a plastic injection molding system thatpermits more efficient space utilization, and hence, permits the use ofgreater numbers mold cavities within set space limitations.

A further object is to provide a plastic injection molding system ascharacterized above in which a plurality of mold cavities are suppliedfrom a single feed passageway so as to reduce the number of passagewaysand heaters that must be provided in the equipment.

Still another object is to provide a unitary torpedo heater that adaptedfor heating the inlet flow to a plurality of mold cavities.

Yet another object is to provide a torpedo heater of the above kind thatis operable for independently controlling the temperature conditions ata plurality of mold cavity gates or inlets.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings in which:

FIG. 1 is a section of a plastic injection mold embodying the presentinvention;

FIG. 2 is an enlarged fragmentary section of the mold shown in FIG. 1taken in the plane of line 2--2;

FIG. 3 is an enlarged longitudinal section of one of the multiple tiptorpedo heaters utilized in the illustrated mold;

FIG. 4 is an enlarged fragmentary section taken in the plane of line4--4 in FIG. 3;

FIG. 5 is a fragmentary section taken in the plane of line 5--5 in FIG.4;

FIG. 6 is a transverse section of the mounting arrangement and leadoutlet for the torpedo heater shown in FIG. 3, taken in the plane ofline 6--6;

FIG. 7 is a transverse section taken in the plane of line 7--7 in FIG.6;

FIG. 8 is a diagrammatic illustration of the electrical winding and leadpin arrangement of the illustrated torpedo heater;

FIG. 9 is a partially diagrammatic section of a plastic injection moldarrangement according to an alternative embodiment of the invention;

FIG. 10 is an enlarged longitudinal section of the multiple tip torpedoheater utilized in the mold arrangement of FIG. 9; and

FIG. 11 is a diagrammatic illustration of the electrical winding andlead pin arrangement of the torpedo heater shown in FIGS. 9 and 10.

While the invention is susceptible of various modifications andalternative constructions, a certain illustrated embodiment thereof hasbeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific form disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions andequivalents falling within the spirit and scope of the invention.

Referring now more particularly to FIGS. 1 and 2 of the drawings, thereis shown an illustrative plastic injection molding system 10 embodyingthe present invention. The system 10 includes a mold 11 and conventionalplastic injection means, including a nozzle 12, for injecting fluidplastic material into the mold. The mold 11 comprises a frame or base 14for supporting a plurality of mold cavity members 15a, 15b and coreinserts 16a, 16b which together define respective part cavities 18a, 18bin a conventional manner. As will be understood by one skilled in theart, the core inserts 16a, 16b each are moveable relative to therespective cavity member 15a, 15b to permit removal of a formed part,and an injector pin 19 (only one which is shown) is provided in eachcore insert to facilitate such part removal. For communicating fluidplastic from the injection nozzle 12 to the cavities 18a, 18b, the moldframe or base 14 is formed with a sprue passageway 20 in communicationwith the nozzle 12, and in this instance, feeds a plurality oftransversely directed runner passageways 21, in this case four innumber. For heating the fluid plastic material in the sprue passageway20, a torpedo heater 22 of a known type is provided, and for heating thematerial in the runner passageways 21, a respective conventional runnertorpedo heater 24 is provided.

In accordance with one aspect of the invention, each runner passagewayfeeds a plurality of sprue passageways and mold cavity gates which areheated by a single torpedo heater in a manner that permits a morecompact and economical mold design for efficient simultaneous molding ofa plurality of parts. To this end, in the illustrated embodiment, eachrunner passageway 21 feeds fluid plastic material to a pair of spruepassageways 25a, 25b and mold cavity gates 26a, 26b which are heated bya respective unitary torpedo heater 30. Since the fluid plastic flowfrom each runner passageway 21 and associated unitary torpedo heater 30are identical, only one will be described in detail.

In keeping with the invention, each torpedo heater 30 has a multiplicityof ends or tips 31a, 31b, in this case two in number, which each areadapted for heating plastic material flowing through a respective spruepassageway 25a, 25b and gate 26a, 26b for a respective mold part cavity18a, 18b. The illustrated torpedo heater 30, as best shown in FIG. 3,has a cylindrical metal casing 32 with one end or tip 31a having anintegrally formed tapered configuration disposed in concentric relationto a tapered entry 34a (FIG. 2) from the sprue passageway 25a to thegate 26a. The opposite end or tip 31b of the torpedo heater 30 is aseparate member of similar tapered configuration affixed to theotherwise open end of the casing 32.

In accordance with a further feature of the invention, the multipletipped torpedo heater 30 is adapted for independent, selectivelycontrolled heating of plastic material flowing through each spruepassageway 25a, 25b and gate 26a, 26b for enhancing the balanced flow ofplastic to the plurality of part cavities 18a, 18b. To this end, theillustrated torpedo heater casing 32 is formed with an elongated bore 36and contains a plurality of selectively controllable heating elements38a, 38b, in this case two in number, adapted for selectively heatingthe molten plastic material in the respective sprue passageways or zones25a, 25b. The heating element 38a comprises a resistance wire 39a woundon a ceramic core 40a that is disposed in one end of the casing bore 36and has a diameter less than the diameter of the bore. The heatingelement 38b in this instance, for reasons which will become apparent,includes a pair of cores 40b, 40b' disposed in the opposite end of thecasing bore 36, with each core having a respective wound resistance wire39b, 39b'. The cores 40a, 40b, 40b' each are interposed between arelatively thin frangible spacers. In this instance, the core 40a isinterposed between an end spacer 42 and a central spacer 44, the core40b' is interposed between the central spacer 44 and an intermediatespacer 45, and the core 40b is disposed between an intermediate spacer46 and an end spacer 48.

The heating elements 38a, 38b each are adapted for independentconnection to an electrical source to permit their selectiveenergization. For this purpose, the heating element 38a has a pair oflead pins or wires 50a, 51a. One end of the resistance wire 39a isconnected to the lead pin 50a adjacent one end of the core 40a and theother end of the resistance wire 39a is connected to the lead pin 51aadjacent the opposite end of the core 40a, as illustrated in FIG. 8. Theheating element 38b similarly has a pair of lead pins 50b, 51b which inthis case extend through the cores 40b, 40b' and the spacerstherebetween. One end of the resistance wire 39b is connected to thelead pin 50b at a point adjacent one end of the core 40b and theopposite end of the wound resistance wire 39b is connected to the leadpin 51b at the opposite end of the core 40b. The opposed ends of theresistance wire 39b' are similarly connected to the lead pins 50b, 51badjacent opposite ends of the core 40b' such that the resistance wires39b, 39b' are electrically connected in parallel across the lead pins50b, 51b.

To facilitate manufacture, the cores 40a and 40b' both are formed withfour lead pin apertures, and the lead pins 50b, 51b, like the lead pins50a, 51a extend through the core 40a and into the end spacer 42, eventhrough the lead pins 50b, 51b are not coupled to the resistance wiresof the core 40a. The lead pins 50a, 51a in the illustrated embodimentneed only extend from the end spacer 42 into the space 55 definedbetween the intermediate spacers 45, 46. Alternatively, the core 40a,like the core 40b, need only be formed with two apertures for therespective lead pins 50a, 51a of that heating element, and the lead pins50b, 51b can be made of shorter length so as to extend only between thespacers 48 and 44. At the location of the spacing 55, the torpedo casing32 is formed with an aperture 56 to permit exiting of the leads from thepins 50a, 51a, and 50b, 51b for connection to an electrical source, aswill become apparent.

It will be appreciated that while in the illustrated embodiment theelectrical resistance wires for the heating element 38b are shownconnected electrically in parallel, alternatively, the resistance wirescould be connected in series. Moreover, while the illustrated torpedoheater has a pair of heating elements 38a, 38b, depending upon thelength of the heater, alternatively greater numbers of axially alignedand independently controlled heating elements could be utilized so as topermit selective heat control at zones intermediate the opposed ends ofthe torpedo heater.

To compensate for irregular heat drains or losses along the length ofthe torpedo heater 30, and thus provide a more uniform heat profile forheating fluid plastic directed through the sprue passageways 25a, 25b,the electrical windings 39a, 39b, 39b', are shaded or concentrated atselected locations. In the illustrated embodiment, the windings 39a and39b both are shaded, as illustrated in FIGS. 3 and 8, adjacent theirrespective tips 31a, 31b. In addition, the winding 39b and 39b' areshaded adjacent the spacing 55 to compensate for additional heat lossesat such location. During manufacture of the torpedo heater 30, heattransmitting material 60, such as magnesium oxide powder or similarmaterial, is deposited in the space between the cores 40a, 40b, 40b' andthe casing bore 36. The assembly preferably is vibrated to pack themagnesium oxide powder tightly within the casing to fill all air voidswithin the assembly. Means, such as an adhesive, may be provided fortemporarily retaining the intermediate spacers 45, 46 in position so asto tightly retain the magnesium oxide powder within the casing.

The assembly of the casing 32 and heating elements 38a, 38b is thenswaged so as to reduce the diameter of the casing bore 36 and compressthe packed magnesium oxide powder within the bore. This provides aneffective heat transfer contact between the heating elements and thecasing for enhancing efficient and uniform heat transfer to the casing.Following swaging, the adhesive or other means utilized for temporarilyretaining the spacers 45, 46 within the casing may be removed, with thespacers 45, 46 being fixedly retained in mounted position by theresulting tight friction force.

For coupling the pairs of lead pins 50a, 51a and 50b, 51b for therespective heating elements 38a, 38b to an electrical source,appropriate pairs of lead wires 61a and 61b are connected thereto. Toindependently control the temperature of the heating elements 38a, 38b,a respective thermocouple probe 62a, 62b is provided for each heatingelement. In the illustrated embodiment, a hypo tube 64a, 64b for eachheating element is disposed adjacent the perimeter of the bore 36 of thecasing and embedded in the magnesium oxide powder 60, and the respectivethermocouple probes 62a, 62b for each heating element is housed withinthe hypo tubes 64a, 64b and extend to a predetermined point in the flowpath for sensing the temperature at such point. It will be understood byone skilled in the art that power to the respective heating element maythereby be selectively controlled in a known manner.

In keeping with the invention, means are provided for permitting theexit of the leads 61a, 61b from the torpedo heater and for supportingthe torpedo heater intermediate its ends in concentric relation in thesprue passageways 25a, 25b so as to permit fluid plastic to be directedonto the torpedo heater at a generally central location, with thematerial then flowing opposite substantially equal distances along thetorpedo heater to the respective part cavity 18a, 18b. To this end, thesupport means in the form of a collar 70 is provided which has aninternal longitudinal aperture 71 substantially greater than the outerdiameter of the torpedo heater casing 32 so as to permit thesubstantially uninterrupted flow of plastic along the torpedo. Thecollar 70 is disposed in off centered longitudinal relation to thetorpedo heater 30, in this case on the left side of the heater, asviewed in FIG. 3. For concentrically supporting the torpedo within thering, in this instance a pin 72 is welded in an aperture in the collar70 and extends inwardly for engaging a topside of the torpedo heater, asviewed in FIG. 3. A bushing 74, also is welded in an aperture in thecollar, extends inwardly for engaging and supporting an underside of thetorpedo heater. The bushing 74 is formed with a central aperture 75 thatcommunicates with the aperture 56 in the torpedo heater casing 32 topermit exiting of the leads 61a and 61b, as well as the leads from thethermocouples 62a, 62b. It will be understood that the bushing 74 mayhave a threaded outer end for receiving the threaded fitting of anappropriate convolute tubing through which the lead wires of the torpedoheater and thermocouples may be trained to the electrical source andcontrol.

In operation of the plastic injection molding system 10, molten plasticis directed from the nozzle 12 into the sprue passageway 20 (FIG. 2) forfeeding the plurality of transversely directed runner passageways 21.Each runner passageway, in turn, feeds a plurality of sprue passageways25a, 25b which can be selectively heated by the respective unitarytorpedo heater 30. The flow of plastic in each sprue passageway 25a, 25bmay be independently controlled for maintaining a balanced flow ofmaterial into the plurality of part cavities 18a, 18b for optimum andefficient operation of the mold. In the event adjustment in temperaturein one sprue passageway is necessary, it may be accomplished withoutaffecting the temperature or flow in the other sprue passageway. The offcentered mounting of the support collar 70 for the torpedo heaterfurther permits the introduction of the fluid plastic onto the torpedoheater at a generally central location so that the flows to therespective part cavities 18a, 18b are substantially the same length.

Referring now to FIGS. 9-11, there is shown a plastic injection moldingsystem 80 embodying an alternative form of the invention. The moldingsystem 80 in this instance includes a multiple tip torpedo heater 81disposed in the path of the flow stream to a mold cavity 82 so that theflow stream passes over the entire length of the heater 81 and ismaintained at the desired, substantially uniform temperature during suchtravel. The molding system 80 includes a manifold plate 84 that may beexternally heated in a conventional manner and is formed with a flowpassageway 85. The flow passageway 85 communicates with the sprue inlet86 of an annular head 88 that is interposed between the manifold plate84 and a central manifold plate 89. A cavity plate 90 is disposed inadjacent relation to the manifold plate 89 and is formed with a gate 91that communicates with the mold cavity 82 defined by the cavity plate 90and a core insert 94.

For heating the fluid plastic flow stream during its travel between thesprue inlet 86 and the gate 91 of the mold cavity 82, the multiple tiptorpedo heater 81 is mounted with one tip disposed adjacent the sprueinlet 86 and the opposite tip disposed adjacent the mold cavity gate 91.The torpedo heater 81, as best shown in FIG. 10, has a cylindricalcasing 95 with one end or tip 96 having an integrally formed taperedconfiguration disposed in concentric relation to a tapered entry fromthe sprue inlet 86. The opposite end or tip 98 of the torpedo heater 80is a separate member of similar tapered configuration affixed to theotherwise open end of the casing 95 and disposed in concentric relationto a tapered entry to the gate 91.

The heater casing 95 is formed with an elongated bore 99 and in thiscase contains heating elements 100a, 100b adjacent each tip for heatinga respective half of the heater. The heating elements 100a, 100b eachcomprise a resistance wire 101a, 101b wound on a ceramic core 102a,102b, which each are interposed between respective pairs of frangiblespacers 104a, 105a and 104b, 105b. Heat transmitting material 106a,106b, such as magnesium oxide powder, is tightly compacted in the spacebetween the cores 102a, 102b and the casing bore 99 in the mannerpreviously described.

In keeping with a further aspect of the invention, the resistance wires101a, 101b for the heating elements 100a, 100b are electricallyconnected in series in order to permit the utilization of heavier gaugeresistance wire for particular applications, and thus enhance thereliability and life of the heater. Such series connection of theheating element resistance wires 101a, 101b has been found to haveparticular advantage in relatively smaller size torpedo heaters whichwould otherwise require relatively fine gauge wire in order to achievethe desired resistive requirements, particularly when connected to a 240volt electrical power source.

To facilitate the series connection of the heating element resistancewires 101a, 101b, a lead pin 115 is provided which extends substantiallythe length of the casing bore 99 through the cores 104a, 104b of bothheating elements. A second lead pin 116a extends through the core 104aof the heating element 100a with one end thereof extending into a space118 between the heating elements, and a third lead pin 116b extendsthrough the core 104b of the other heating element 100b with one endthereof similarly extending into the space 118 between the heatingelements. As best illustrated in FIG. 11, the resistance wire 101a forthe heating element 100a has one end connected to the lead pin 115 andits other end connected to the lead pin 116a. The resistance wire 101bfor the heating element 100b has one end connected to the lead pin 115which is common to the heating element 100a and its other end connectedto the lead pin 116b. The lead pins 116a and 116b in turn are connectedto a power source through lead wires 119a, 119b, with the result thatthe current flows in series through the resistive wires 101a, 101b ofthe heating elements. A thermal couple probe 120 is provided for sensingthe temperature at one of the tips to permit proper control of theoperating temperature of the heating elements.

The lead wires 119a, 119a and thermal couple 120 exit through an opening121 in the casing 95 and centrally through a bushing 122 of a supportcollar 124 in a manner similar to that previously described, except thatin this instance the opening 121 and bushing 122 are located at acentral location along the length of the torpedo heater. It will beunderstood that the ends of the collar 124 are maintained in sealedrelation between the annular head 88 and cavity plate 90 between whichit is disposed.

In operation of the mold system 80, the melt stream is directed over theentire length of the torpedo heater 81 between the sprue inlet 86 andmold cavity gate 91. By appropriately shading the windings of theheating elements 100a, 100b, as previously described, a substantiallyuniform heat profile may be generated along each heating element. Sincethe heating elements 100a, 100b in this case are substantiallyidentical, as the melt stream passes over the length of the torpedoheater it may be maintained at the desired uniform temperature with ahigh degree of accuracy and efficiency.

From the foregoing, it will be appreciated by one skilled in the artthat the present invention provides a relatively compact and efficientlyoperable plastic injection molding system. The system further permitsmore efficient space utilization, by permitting single runnerpassageways to each communicate with plurality of sprue passageways,which in turn can be heated by multiple tip torpedo heaters. Themultiple tip torpedo heater furthermore has a relatively compact andeconomical design which lends itself to easy and versatile installationand efficient operation.

I claim as my invention:
 1. A plastic injection molding systemcomprising means defining a generally cylindrical bore with taperedopposite ends communicating with respective small diameter gates throughwhich fluid plastic material is directed,means defining a mold cavity incommunication with at least one of said gates, a composite torpedoheater comprising an elongated, metal casing having a non-electricallyheatable, exposed outer surface with a tapered, pointed tip at oppositeoutermost ends thereof, means supporting said torpedo heaterconcentrically in said bore with said tips each in closely adjacentrelation to one said gates and with said outer exposed casing surfaceand said bore defining an unobstructed annular fluid plastic flowpassageway about each said tip and a portion of said casing adjacentsaid tip and substantially along the entire length of said casingthrough which fluid plastic material is directed at an elevatedtemperature, said annular flow passageway having a radial width definedby the distance between the outer perimeter of said casing and the innerperimeter of the cylindrical bore that is less than the diameter of saidcasing; said casing being formed with an internal bore at the locationof each said tip, said casing having an outer diameter of about twicethe diameter of said casing bore so as to define a thick casing wallabout the bore, electrical heating means disposed in the bore of eachtip, said heating electrical means comprising a core with a resistancewire disposed thereon and heat transmitting material surrounding thewire and core, said heat transmitting material being compacted about theresistance wire and core for filling all air voids therebetween andeffecting efficient heat transfer; means exiting said casingintermediate the ends thereof for electrically coupling said heatingmeans to a power source for enabling heating of said heating means andheat conduction outwardly through said thick casing wall for heatingfluid plastic material directed through said flow passageway and oversaid tips to a desired temperature independent of temperature conditionsexternal to said casing, and means for controlling the temperature ofsaid heating means and thus the temperature of said tips and fluidplastic material directed through said passageway and over said tips. 2.The plastic injection molding system of claim 1, in which saidelectrical heating means includes an individual electrical heatingelement disposed in the bore of each said tip.
 3. The plastic injectionmolding system of claim 1 in which said heating elements each haveconnector pins extending through the cores thereof, said heating elementresistant wires being connected to selected of said pins, and means forcoupling said pins to said power source.
 4. The plastic injectionmolding system of claim 3 in which the resistance wires for said heatingelements are connected to respective individual pairs of said connectorpins.
 5. The plastic injection molding system of claim 3 in which saidresistance wires for said heating elements are electrically connected inseries with said connector pins.
 6. The plastic injection molding systemof the claim 1 in which said bores are disposed in axially spacedrelation to each other, said casing being formed with an apertureadjacent the spacing between said cores, the lead pins for each heatingelement extending to a location adjacent said casing aperture, and saidelectrical coupling means includes means extending through said casingaperture for connecting said lead pins to said power source.
 7. Theplastic injection molding system of claim 1 in which said electricalheating element means includes an individual electrical heating elementdisposed in the bore of each said tip.
 8. A plastic injection moldingsystem comprising a mold having first passageway means into which afluid plastic flow stream is introduced, said first passageway meanscommunicating with a sprue passageway, said sprue passageway, beingformed by a cylindrical bore with tapered opposite ends communicatingwith respective small diameter gates through which fluid plasticmaterial is directed; means defining mold cavities in communication withsaid gates;a composite torpedo heater comprising an elongated metalcasing having an exposed outer cylindrical surface with tapered, pointedtips at opposite outmost ends thereof; means supporting said torpedoheater concentrically in said sprue passageway bore with said tips eachin closely adjacent relation to one of said gates and with said outerexposed casing surface and said bore defining an unobstructed annularfluid plastic flow passageway about each said tip and a portion of saidcasing adjacent said tip and substantially along the entire length ofsaid casing through which fluid plastic material is directed at anelevated temperature; said annular flow passageway having a radial widthdefined by the distance between the outer perimeter of said casing andthe inner perimeter of the cylindrical bore that is less than thediameter of said casing; said casing being formed with an internal boreat the location of each said tip; said casing having an outer diameterof about twice the diameter of said casing bore so as to define a thickcasing wall about the bore, electrical heating means disposed in thebore of each said tip; said heating means comprising a core with aresistance wire disposed thereon and heat transmitting materialsurrounding the wire and core, said heat transmitting material beingcompacted about the resistance wire and core for filling all air voidstherebetween and effecting efficient heat transfer; means existing saidcasing intermediate the ends thereof for electrically coupling saidheating means to a power source for enabling heating of said heatingmeans and heat conduction outwardly through said thick casing wall forheating fluid plastic material directed through said annular flowpassageway and over said tips to a desired temperature independent oftemperature conditions external to said casing; and means for regulatingthe temperature of said heating means and thus the temperature of saidtips and fluid plastic material directed through said annular flowpassageway and over said tips.
 9. The plastic injection molding systemof claim 8 in which said supporting means comprises a collar locatedintermediate the ends of said casing and having an aperturesubstantially greater than the diameter of said casing for receivingsaid casing while permitting fluid material flow between said casing andcollar, and retaining means for holding said casing concentricallywithin said collar.
 10. The plastic injection molding system of claim 9in which casing is formed with an aperture, said retaining meansincluding a radially disposed bushing member having an aperturecommunicating with said casing aperture through which said electricalcoupling means extends.
 11. The plastic injection molding system ofclaim 9 in which said collar is disposed at an off-centered locationalong the longitudinal axis thereof.
 12. The plastic injection moldingsystem of claim 11 including means for introducing fluid plasticmaterial into the sprue passageway within which said torpedo heater isdisposed at an approximate central location along said torpedo heatercasing.